1. Field of the Invention
The present invention relates to a technology for detecting a liquid discharge failure in an inkjet recording apparatus.
2. Description of the Related Art
A typical inkjet printer includes a liquid-discharge-failure detecting device for detecting an ink discharge failure. For this purpose, the inkjet printer includes a light-emitting unit and a light-receiving unit. The light-emitting unit emits a detection beam toward an ink droplet. The light-receiving unit is located at a position offset from an optical axis of the detection beam to receive a scattered light generated by scattering of the detection beam by the ink droplet. The liquid-discharge-failure detecting device optically detects an ink discharge failure by using data pertaining to the scattered light received by the light-receiving unit.
Such an inkjet printer is disadvantageous in that a detection beam that strays inside the inkjet printer as a stray light can enter the light-receiving unit after being reflected from a head nozzle surface of an inkjet head or the like, which may result in faulty detection. Various techniques have been proposed for avoiding such faulty detection. An example of such a technique is disclosed in Japanese Patent Application Laid-open No. 2006-7447. According to this technique, an aperture member having an aperture is provided immediate upstream of a light-receiving unit along an optical path so that unnecessary detection beam reflected from a head nozzle surface of an inkjet head or the like is blocked by the aperture member and only necessary the scattered light passes through the aperture.
Moreover, occurrence of optical diffraction can lead to incorrect detection of an ink discharge failure. To this end, Japanese Patent Application Laid-open No. 2006-7447 discloses increasing the amounts of liquid discharged through nozzles at positions near the light-receiving unit than those discharged through the other nozzles.
However, it is difficult to employ this technique for a wide inkjet head. This technique also disadvantageously requires complicated processing to perform liquid discharge control, decreases durability of a specific nozzle(s), and increases an amount of ink required for detection.